Stirling cycle engine power control system

ABSTRACT

A system for controlling power in a Stirling Engine System by varying the effective volume of a working chamber which has a control chamber with a movable wall controlled by fluid pressure connected to vary the volume of working chamber. The fluid pressure is controlled by selectively connecting a reservoir of fluid under pressure to the control chamber by a control valve to increase or decrease the pressure and accordingly the volume of the control chamber.

United States Patent 91 [111 3,820,330 Hakansson June 28, 1974 STIRLING CYCLE ENGINE 3,559,398 2/1971 Meijer et al. 60/24 CO O SYSTEM I l gaspershet al. 60/24 [75] Inventor: Sven Anders Samuel H n I ennet um 60/24 Malmo Sweden Primary Examiner-Edgar W. Geoghegan [73] Assignee: Kommanditbolaget United Stirling Assistant Examiner-H. Burks, Sr.

(SSwtden) AB & Co., Malmo, Attorney, Agent, or Firm-Laurence R. Brown we en [22] Filed: Oct. 17, 1972 I [57] ABSTRACT PP FIG-$298,342 A system for controlling power in a Stirling Engine System by varying the effective volume of a working 52 us. Cl. ..60/521 chamber which has a whim chamber with a hm/able [51] Int. Cl. F02 1/ 04 wan controlled by fluid pressure connected to vary the [58] Field of Search 60/24 volume of h chamhe" h fluid is 1 trolled by selectively connecting a reservoir of fluid [561 CM 2:12t:222;;szsszcizzztzs zsze znz22x2 3 458 995 Z Q PIATENTS 60/24 ingly the volume of the control chamber.

C ner et a 3,554,672 I/ 1971 Brandes 60/24 9 Claims, 2 Drawing Figures 1 STIRLING CYCLE ENGINE POWER-CONTROL SYSTEM This invention relates to a Stirling cycle engine power-control system of the kind (herein called the kind defined) in which one of the working spaces in each cylinder of the engine is connected to a chamber having variable volume.

Some known systems of the kind defined contain valves for regulating the flow of working gas between the working chamber of the Stirling cycle engine and the chamber having variable volume in order to adjust the amount'of effective variable volume.

The object of the present invention is to provide an effective control system of a simple design rendering a high degree of efficiency on partial loads on the engine and a very rapid response to input signals requiring changes inengine power or output.

According to the present invention there is provided a power-control system of the kind-defined characterised in that said chamber having variable volume is provided with at least one movable wall which-is counterbalanced by a pressure fluid incommunication with a reservoir for said fluid through two separate branch conduits, each containing a respective non-return valve, and control valve means for selectively allowing the blocking of both of said branch conduits vor the connecting alternatively of either one or the other of said branch conduits with said fluid reservoir.

The scope of the monopoly sought is defined in the claims hereinafter, and how the invention may be put into practice is described in more detail with reference to the accompanying drawing in which FIG. 1 shows a diagram of a power-control system for a Stirling cycle engine and 7 FIG. 2 shows a modified detail of the system shown in FIG. 1.

The basic working principle of a Stirling cycle engine- (not shown in the drawing) consists in compressing a gas in a working chamber at a low temperature, moving the gas to a high-temperature working chamber while heating the gas, and letting the gas expand to produce a mechanical work, transferringthe gas back to the first-mentioned working chamber while cooling the gas, and then compressing the gas while absorbing some mechanical work in preparation for the cycle to be repeated.

The power or output which may be produced by the engine depends on several factors, one of them being the pressure variations of the working gas. By connecting one of the working chambers preferably the low temperature chamber with a space not varying in volume during the Stirling cycle, the pressure variations in the gas during the cycle may be decreased and thereby the engine power or output can be reduced.

In FIG. 1 the reference numerals l a and l b both indicate one chamber, which is the working chamber 1 having low temperature, but 1 a and 1 b represent this single working chamber at two differentmoments. l a represents the working chamber 1 during a period when the pressure of the working gas is above the average value whereas 1 b represents the same chamber 1 during a period when the gas pressure is below the average value. The reference numerals 2 a and 2 b designate a single tank 2 at corresponding periods. The working chamber 1 and the tank 2 are interconnected by a conduit 3 (shown twice in FIG. 1) which is always open for gas flow in both directions.

The said tank 2 contains a flexible wall or a piston 4 dividing the interior of the tank into two separate chambers 5 and 6, the chamber 5 containing working gas whereas the chamber 6 is filled with oil. The chamber 6 is connected to a reservoir 7 through two branch pipes 8 and 9 each containing a respective non-return valve 10 or 11. The non-return valve 10 in the pipe 8 allows flow of oil only into the chamber 6, whereas the non-return valve 11 in the pipe 9 only allows flow of oil only in the direction from the chamber 6. A control valve slide having three sections 12,13 and 14 may selectively block or allow the communication between the reservoir 7 and the chamber 6 or it may establish such connection alternatively through either the pipe 8 or the pipe 9.

In most Stirling cycle engines a buffer space is established under each working piston of the engine. This buffer space contains working gas at low temperature and does not actively take part in the Stirling cycle. Its function is merely to act as a counter-load on the piston rods, the connection rods and the crank shaft. The pressure in the buffer space is normally somewhat higher than the mean effective pressure of the working gas.

In FIG. 1 the said buffer space is indicated by the reference numeral 15, and it is connected to the lowtemperature working chamber 1 through a conduit 16 containing a non-return valve allowing flow in the direction towards the buffer space 15 only. However, in case the mean pressure of the gas in the working chamber 1 is lowered due to an increase of the volume in the chamber 5 it also is desirable to lower the mean pressure in the buffer space 15. This is automatically effected by a valve 17 having three connections 18, 19 and 20. The connection 18 communicates continually with the buffer space 15. The connection 19 communicates continually with pipe 9. The connection 20 communicates with a pipe 21 leading to the low temperature working chamber, but this pipe 21 contains a nonretum valve 22 allowing only flow in the direction into the low temperature working chamber 1. A floating valve member23 in the valve 17 will normally close the connection 20.

It will be appreciated that in practice the system illustrated by FIG. 1 comprises only one each of the parts 1, 2, 3, 4, 5, 6, 8, 9, 10, ll, 16 and 22, and that these parts are each represented twice in FIG. 1 in order to conveniently illustrate two different stages of the working cycle.

The power-control system illustrated in FIG. 1 will operate as follows:

It is assumed that initially the valve slide 12, 13 and 14 is located in the position shown, in which the connection between the reservoir 7 and the chamber 6 is disconnected. During operation of the Stirling engine the pressure in the low temperature working chamber 1 will vary, the reference numeral 1 0 illustrating pressures above the average and the reference numberal 1 b illustrating pressures below the average.

The pressures in the chambers 5 and 6 will follow the pressure in the low temperature working chamber, but the pressure in the branch pipe 8 leading to the valve slide 12, 13, 14 will remain constant at the minimum pressure level whereas the pressure in the other branch pipe 9 leading to the said valve slide will remain atthe mairimum pressure level.

It is now assumed that it is desired to increase the power of the Stirling cycle engine. The slide 12, 13, 14 is moved upwards and thus the section 12 will allow a communication between the reservoir 7 and the chamber 6 through the low pressure pipe 8 allowing flow of oil in the direction towards the chamber 6 only. The volume of the chamber 6 will now increase and the chamber will decrease in volume, thereby causing an increase of the power of the Stirling cycle engine. The mean effective pressure of the gas in the Stirling cycle will also increase and so will the pressure in the'bufler space 15 due to its connection with the low temperature working chamber through the conduit 16 containing a non-return valve allowing flow only in the direction towards the buffer space 15.

In case it is desired to decrease the power output of the engine the slide 12, 13, 14 is moved downwards, whereby the section 14 will cause a communication between the reservoir 7 and the chamber 6 via the high pressure pipe 9 allowing flow of oil in the direction towards the reservoir 7 only. The volume of the chamber 6 will decrease and the volume of the chamber 5 will increase, thus causing a decrease of engine power. The mean pressure of gas during the Stirling cycle will decrease, and the valve member 23 will move downwardly, thereby opening the connection allowing flow of gas from the buffer space 15 into the working chamber 1. Thus the pressure difference between the buffer space 15 and the working chamber 1 will be kept within certain limits regardless of the engine power output.

In FIG. 1 the pressure in the reservoir 7 is counterbalanced by a spring-loaded piston 24, the springloading being effected by belleville washers 25 causing a force which decreases with the compression of the springs. A similar power could be obtained by using a gaseous medium as a spring and designing the piston to have a decreasing effective area as the piston travels in the direction to increase the effective volume of the reservoir 7.

FIG. 2 shows a modified embodiment of the control valve slide 12, 13, 14 and the use of a pump having a delivery pipe 31 and a suction pipe 32. The low pressure pipe 8 and the high pressure pipe 9 as well as the connection to the reservoir 7 are shown again. It will be understood that in the position shown the slide section 13 will disconnect the reservoir 7 from both pipes 8 and 9. In case the slide l2, 13, 14 is moved upwards the suction pipe 32 leading to the pump 30 will be connected to the pipe 9 allowing oil to flow from the chamber 6 into the pump 30 and through the pipe 31 and the valve section 12 into the reservoir 7. Hereby the power output of the engine will be decreased.

In case the power output of the engine is desired to be increased, the slide 12, 13, 14 is moved downwards, causing a connection between the delivery pipe 31 and the pipe 8 allowing flow into the chamber 6. Simultaneously the suction side of the pump 30 will be connected to the reservoir 7'.

The movements of the control valve slide may be regulated or caused in any desired manner, for example through a hand lever or a pedal or a servo-mechanism responsive to signals from an engine governor or any other source.

The system with the modification according to FIG. 2 may cause a more rapid reaction to signals requiring changes in the engine power output.

What we claim is:

l. A Stirling cycle engine system having a working space with different pressures generated therein, a chamber of variable volume connected to said working space, means in said chamber to change its volume comprising a wall movable under pressure of a fluid, means for selectively moving said wall comprising a reservoir source of fluid under pressure, two separate branch conduits coupling said reservoir to said chamber, a non-return valve in each of said branch conduits permitting flow respectively in opposite directions, and control valve means operable selectively to connect one or none of saidbranch circuits between said chamber and said reservoir.

2. A system as defined in claim 1 wherein said control valve meanscomprises a single movable valve slide.

3. A system as defined in claim 1 including a pump adapted to pump fluid in either of two directions, and wherein said control valve means selectively connects said pump into the branch circuits between said chamber and said reservoir to pump said fluid in a single direction therebetween.

4. A system as defined in claim 1 wherein said reservoir includes pressure control means causing a force which decreases as the source or fluid in said reservoir increases.

5. A system as defined in claim 4 wherein said pressure control means comprises means spring loaded by belleville washers.

6. A system as defined in claim 1 wherein a said buffer space is connected to said working space by means of a conduit containing a non-return valve allowing flow only in the direction towards the buffer space, and further automatic valve control means communicating between said buffer space and said working space connected with a conduit including a non-return valve in the direction toward said working space, said automatic valve control means normally closing said latter conduit, and means operating said automatic valve to open said latter conduit when the pressure in the working chamber is lowered to a predetermined value.

7. A Stirling cycle engine system having a working chamber with different pressures generated therein, a closed system confining working gas from said working chamber and including a single chamber of variable volume with a path for said working gas to flow in both directions from said working space to said chamber, means in said chamber to change its volume comprising a wall under pressure of a fluid, a source of fluid under pressure, and control means for changing the fluid pressure to change the volume of said chamber and thereby control the power output of said engine system.

said single chamber in a single direction. 

1. A Stirling cycle engine system having a working space with different pressures generated therein, a chamber of variable volume connected to said working space, means in said chamber to change its volume comprising a wall movable under pressure of a fluid, means for selectively moving said wall comprising a reservoir source of fluid under pressure, two separate branch conduits coupling said reservoir to said chamber, a non-return valve in each of said branch conduits permitting flow respectively in opposite directions, and control valve means operable selectively to connect one or none of said branch circuits between said chamber and said reservoir.
 2. A system as defined in claim 1 wherein said control valve means comprises a single movable valve slide.
 3. A system as defined in claim 1 incLuding a pump adapted to pump fluid in either of two directions, and wherein said control valve means selectively connects said pump into the branch circuits between said chamber and said reservoir to pump said fluid in a single direction therebetween.
 4. A system as defined in claim 1 wherein said reservoir includes pressure control means causing a force which decreases as the source or fluid in said reservoir increases.
 5. A system as defined in claim 4 wherein said pressure control means comprises means spring loaded by belleville washers.
 6. A system as defined in claim 1 wherein a said buffer space is connected to said working space by means of a conduit containing a non-return valve allowing flow only in the direction towards the buffer space, and further automatic valve control means communicating between said buffer space and said working space connected with a conduit including a non-return valve in the direction toward said working space, said automatic valve control means normally closing said latter conduit, and means operating said automatic valve to open said latter conduit when the pressure in the working chamber is lowered to a predetermined value.
 7. A Stirling cycle engine system having a working chamber with different pressures generated therein, a closed system confining working gas from said working chamber and including a single chamber of variable volume with a path for said working gas to flow in both directions from said working space to said chamber, means in said chamber to change its volume comprising a wall under pressure of a fluid, a source of fluid under pressure, and control means for changing the fluid pressure to change the volume of said chamber and thereby control the power output of said engine system.
 8. A system as defined in claim 7 wherein said path comprises an open conduit between said working chamber and said chamber of variable volume.
 9. A system as defined in claim 7 wherein said control means comprises two conduits with one way valve means between said source of fluid and said wall and selector means for choosing a single one of said conduits to permit fluid to flow between said source and said single chamber in a single direction. 